TCPMP plays MP4s but not ones encoded for Ipods too well. I found that for certain MP4's it's still a bit choppy even on my 624mhz Axim. In order to play MP4 video's smoothly, I found that Coreplayer (
CorePlayer - Home) plays them properly. They're basically the commercial spin off of the TCPMP project. One bad thing about Coreplayer was that the TCPMP Flash plug-in did not work on it. So for now I'll stick with both players on my device.